Using bootfw.zip from a USB drive will only work for secure laptops,
or unsecure laptops with the X key held down. This is coded in the
firmware. Since you must use unsecure laptops, because of your
customiser, this code is skipped.
Using bootfw.zip on internal storage will work in the same way, coded
in the firmware. But in the case where the laptop is unsecure and the
X key is not held down, the OLPC OS provided file int:\boot\olpc.fth
triggers the process instead.
So you could use your post-install customiser to copy the bootfw.zip
file in /boot, and on next power cycle it will be reflashed.
I advise, however, that you leave the file in u:\boot\bootfw.zip and
hold down the X key on first boot, then hold down the four game keys
on second boot. This will mean the firmware will upgrade first, while
you are there and watching.
If you have volunteers who can't cope with that precaution, continue
with the four game key method.
--
James Cameron
http://quozl.linux.org.au/